/Engine/Plugins/Runtime/Metasound/Source/MetasoundFrontend/Public/MetasoundParameterPack.h
Here is the proxy thatUMetasoundParameterPackcreates when asked for a proxy by the audio system.
class FMetasoundParameterPackProxy : public [Audio::TProxyData< FMetasoundParameterPackProxy >](API\Runtime\AudioExtensions\TProxyData)